JP2012180675A - Natural ground situation prediction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a natural ground situation prediction method and a tunnel boring method, capable of boring a tunnel while easily predicting the situations of natural ground in front of a face as daily construction management.SOLUTION: The natural ground situation prediction method includes: a first step of performing a work of setting a face side measurement point on a first measurement cross section and setting a pit mouth side measurement point separated from the face side measurement point to the pit mouth side by a distance a, a work of measuring an initial value which is the positional relation between the face side measurement point and the pit mouth side measurement point, a work of measuring a measurement value which is the positional relation between the face side measurement point and the pit mouth side measurement point at a stage that a face K reaches a position separated from the measurement cross section by a distance b, and a work of calculating relative displacement which is a difference between the initial value and the measurement value; and a second step of calculating the relative displacement similarly to the first step after the face K passes through a second measurement cross section. On the basis of comparison between the relative displacement calculated in the first step and the relative displacement calculated in the second step, the natural ground situation in front of the face K is predicted.

Description

  The present invention relates to a natural ground condition prediction method for predicting a natural condition in front of a face.

  In the construction of a mountain tunnel, if the state of the ground in front of the face can be grasped in advance, excavation can be carried out more safely and more economically.

  In the construction of tunnels, ground conditions such as ground reconnaissance and elastic wave exploration from the ground surface are predicted in advance in the planning and design stages. In the survey, it was difficult to fully understand the ground conditions of the tunnel, which is a linear structure.

  Therefore, a method (so-called information-based construction) that ensures safety and economics of construction while observing and measuring ground conditions at the construction stage and modifying the prior design and construction methods as appropriate is standard practice. It has been broken.

  In addition, when excavating areas where there is a high possibility that defective grounds such as fault crushing zones and high-pressure spring zones are present based on the results of prior ground surveys, defective sites in front of the face at the construction stage are to be excavated. Surveys such as advanced drilling and underground elastic wave exploration may be conducted to grasp the exact location, scale, and strength characteristics of the mountain.

  For the purpose of such computerized construction and daily construction management, it is standard practice to carry out downhole displacement measurements, such as top-end subsidence measurement and internal displacement measurement, at regular intervals in the tunnel longitudinal direction. ing. It is common to use a total station for downhole displacement measurement. By using the total station, it is possible to relatively easily obtain the displacement in the tunnel axis direction as well as the tunnel transverse direction and the vertical direction.

For example, Non-Patent Document 1 discloses a method for predicting the state of a natural ground in front of the face by the tendency of increase or decrease of these displacement amounts.
Patent Document 1 discloses a method for determining the presence or absence of a weak geological zone in front of the face using measurement results in three-dimensional directions of tunnel axial displacement, tunnel transverse vertical direction and tunnel transverse horizontal direction. Yes.

Japanese Patent No. 3856392

W. Schubert et al., “The importance of longitudinal deformation in tunnel excavation”, “Processings of the 8th International Congestion Rock Rock Mechanics, Tokio. A. Balkema, 1995, p. 1411-1414

  However, advanced boring and underground elastic wave exploration are operations near the face and it is necessary to interrupt the excavation work of the tunnel, which causes an influence on the entire construction period. In addition, since it takes a lot of setup and labor, it was difficult to implement as part of daily construction management.

  Displacement measurement using the total station involves surveying work at the time of measurement, and it is necessary to interrupt the excavation work.Therefore, when trying to carry out more accurate measurement by closely measuring frequency and measurement interval, There was a risk of affecting the overall construction period.

  A comparatively high-accuracy total station is used for downhole measurement, but the distance measurement accuracy is about 3 mm. Therefore, when the measured displacement is smaller than that, the displacement behavior of the natural ground may not be captured due to the measurement error.

  The present invention is intended to solve the above-described problems, and predicts a ground condition that enables tunnel excavation while easily and accurately predicting the condition of the ground in front of the face. The problem is to propose a method.

  In order to solve the above-mentioned problem, the ground state prediction method of the present invention sets a face-side measurement point in the first measurement section and at the well-side measurement point separated from the face-side measurement point by a distance a from the face side. A work for measuring an initial value that is a positional relationship between the face-side measurement point and the well-side measurement point, and a stage where the face has reached a position separated by a distance b from the measurement cross section, A first step of performing an operation of measuring a measurement value that is a positional relationship between a face-side measurement point and the wellhead-side measurement point, and an operation of calculating a relative displacement that is a difference between the initial value and the measurement value; After the face passes through the second measurement cross section, the second step of calculating the relative displacement in the same manner as the first step, the relative displacement calculated in the first step and the relative displacement calculated in the second step, Predict the ground conditions ahead of the face based on the comparison of It is characterized.

  In the natural ground condition prediction, when the relative displacement calculated in the second step is larger on the compression side than the relative displacement calculated in the first step, it is predicted that a soft layer exists ahead of the face, and the second What is necessary is just to estimate that a hard layer exists ahead of the face when the relative displacement calculated in the process becomes larger on the tension side than the relative displacement calculated in the first process.

According to such a natural ground condition prediction method, since the state of the natural ground ahead of the face can be grasped in advance, tunnels can be excavated by a construction method according to the natural condition and safer and more economical construction is possible. It becomes possible.
Since the relative displacement in the tunnel axis direction between the two points is measured, it is possible to use a highly accurate measuring device, and therefore it is possible to measure with high accuracy.

  According to the natural ground condition prediction method of the present invention, it is possible to excavate a tunnel while predicting the natural condition in front of the face in a simple and highly accurate manner.

(A)-(c) is a longitudinal cross-sectional view which shows each step of the natural ground condition prediction method which concerns on this embodiment. (A) is a cross-sectional view which shows the installation condition of a target, (b) is a cross-sectional view which shows the installation condition of a laser displacement meter. It is a figure which shows the analysis result in the case of excavating the natural ground provided with the stratum boundary which changes from a hard layer to a soft layer, (a) is an axial relative displacement at the time of measurement distance 20m, and from a measurement section to a stratum boundary It is a figure which shows the relationship with a distance, (b) is a figure which shows the relationship between the axial direction relative displacement at the time of measurement distance 1m, and the distance from a measurement cross section to a stratum boundary. It is a figure which shows the analysis result in the case of excavating the natural ground provided with the stratum boundary which changes from a soft layer to a hard layer, (a) is an axial relative displacement at the time of measurement distance 20m, and from a measurement section to a stratum boundary It is a figure which shows the relationship with a distance, (b) is a figure which shows the relationship between the axial direction relative displacement at the time of measurement distance 1m, and the distance from a measurement cross section to a stratum boundary.

Embodiments of the present invention will be described with reference to the drawings.
The tunnel excavation method of this embodiment is to excavate the tunnel T after predicting the situation of the natural ground ahead of the face K by the natural condition prediction method.

As shown in FIG. 1, the natural ground condition prediction method measures the relative displacement between two points installed in the tunnel T, and predicts the natural ground condition in front of the face K by the change of the relative displacement accompanying the excavation. It is a thing, Comprising: The 1st process, the 2nd process, and the natural ground prediction process are provided.
The first process includes a first installation work, a first initial value measurement work, a first measurement work, and a first calculation work. Further, the second process includes a second installation work, a second initial value measurement work, a second measurement work, and a second calculation work.

  In the first installation work, as shown in FIG. 1A, the first wing-side measurement point is set on the measurement section D1 (first measurement section), and the first wing-side measurement point is connected to the wellhead side ( A measurement point on the first wellhead side that is a distance a away from the face K) is set.

  In the present embodiment, when the face K reaches a position 1 m ahead of the measurement cross section D1, the target 1 is installed at the first wing-side measurement point, and the laser displacement meter 2 is provided at the first wellhead-side measurement point. Install. In addition, the timing which installs the target 1 will not be limited if it is after the face K passes the measurement cross section D1. Moreover, the timing which installs the laser displacement meter 2 will not be limited if it is after the face K passes the 1st wellhead side measurement point.

  The target 1 is fixed to the surface of the shotcrete 3 of the tunnel T as shown in FIG. In this embodiment, it is installed above the predetermined height h (1.5 m in this embodiment) from the spring line SL of the tunnel T. In addition, the installation location of the target 1 is not limited, The top end of the tunnel T may be sufficient and a side wall part may be sufficient. Moreover, the target 1 does not necessarily need to be attached to the shotcrete 3, and may be attached to, for example, a natural wall surface or a steel support.

  The laser displacement meter 2 is fixed to the surface of the shotcrete 3 of the tunnel T as shown in FIG. In the present embodiment, like the target 1, it is installed above a predetermined height h (1.5 m in this embodiment) from the spring line SL of the tunnel T. In addition, although the installation location of the laser displacement meter 2 is not limited, it is desirable to install the laser displacement meter 2 so that the straight line connecting the target 1 and the laser displacement meter 2 is parallel to the tunnel axis.

In the first initial value measurement operation, the initial value (first initial value) L of the positional relationship (separation distance) between the first wing-side measurement point (target 1) and the first wellhead-side measurement point (laser displacement meter 2). Measure ₀ .

The measurement of the first initial value L ₀ is basically performed immediately after the target 1 and the laser displacement meter 2 are installed. In order to suitably perform the natural ground prediction, it is desirable that the working face K to practice the measurement of the initial value L ₀ as soon as possible after passing through the measuring section D1.

In the first measurement operation, as shown in FIG. 1 (c), distance (first measure) of the target 1 and the laser displacement meter 2 with further Horisusumeru the tunnel T to measure L _n. In the present embodiment, the first measurement is performed at a stage where the distance between the face K and the measurement cross section D1 reaches a predetermined distance b (b ₁ , b ₂ ,...) (For example, every 1 m is dug). The values L _n (L ₁ , L ₂ ,...) Are measured.

Measurement of the first measurement value L _n is performed until the separation of the working face side measuring point D1 and the working face K is a constant distance (e.g., 20 m). The measurement of the first measurement value L _n, the distance between the measuring section D1 and the working face K is increased, may be performed until the first relative displacement ΔL to be described later is found that nearly a constant value.

In the first calculation work, a first relative displacement ΔL _n (axial relative displacement) is calculated by comparing the first initial value L ₀ and the first measured value L _n (see Equation 1). When ΔL _n is positive, it is called the axial relative displacement on the tension side, and when ΔL _n is negative, it is called the axial relative displacement on the compression side.
ΔL _n = L _n −L ₀ Formula 1

  In the second installation work, after the face K passes the second measurement section (measurement section D1), a second face side measurement point is set in the measurement section D1, and a distance a from the second face side measurement point to the wellhead side. Set the second well side measurement point that is only a distance away.

In this embodiment, as shown in FIG. 1A, when the face K reaches a position 1 m ahead of the measurement section D1, the target 1 is installed at the second face measurement point, and the second wellhead side A laser displacement meter 2 is installed at the measurement point. In addition, the timing which installs the target 1 will not be limited if it is after the face K passes the 2nd measurement cross section. The timing for installing the laser displacement meter 2 is not limited as long as the face passes after the second wellhead side measurement point.
In addition, the installation method of the target 1 and the laser displacement meter 2 is performed similarly to the method of installing the target 1 and the laser displacement meter 2 at the first wing side measurement point and the first wellhead measurement point.

The measurement of the second initial value M ₀ is basically performed immediately after the target 1 and the laser displacement meter 2 are installed. The timing when measuring a second initial value M ₀ include, but are not limited to, a distance c from the second measuring section to the working face K is, when measuring the first initial value L ₀ first The distance c is preferably the same as the distance c from the measurement cross section to the face K (see FIG. 1B).

In the second measurement operation, as shown in FIG. 1C, the tunnel T is further dug, and the target 1 and the laser displacement meter 2 are separated when the distance between the face K and the measurement cross section D1 becomes the distance b. The separation distance (second measured value) M _n is measured. In the present embodiment, apart distance _{b (b 1, b 2,} ...) of the working face K and the measuring section D1 second in since step (for example, every to 1m excavation) measurement _{M n (M 1, M 2} , ...) is measured. Note that the timing for measuring the second measurement value M _n is desirably the same as the timing for measuring the first measurement value L _n .

The measurement of the second measurement value _Mn is performed until the distance between the second face measurement point and the face K reaches a certain distance (for example, 20 m). The measurement of the second measurement value M _n may be performed until the distance between the measurement cross section D1 and the face K is increased and it is recognized that the second relative displacement ΔM described later becomes a substantially constant value.

In the second calculation work, the second relative displacement as compared to the second initial value M ₀ and the second measured value M _n (relative axial displacement) is calculated .DELTA.M _n (see Equation 3).
ΔM _n = M _n −M ₀ Formula 3

The natural ground prediction step is based on the difference between the first relative displacement ΔL _n calculated in the first step and the second relative displacement ΔM _n calculated in the second step. This is a prediction process.
Note that the first relative displacement ΔL _n and the second relative displacement ΔM _n used for the prediction of ground conditions are measured values when the distance from the face K at the time of measurement is the same distance b (for example, distance b = 10 m). L _n and M _n are used.

When the second relative displacement ΔM _n is larger than the first relative displacement ΔL _n on the compression side (ΔL _n > ΔM _n ), it is predicted that a soft layer exists ahead of the face K, and the second relative displacement ΔM _n is When it becomes larger than the first relative displacement ΔL _n on the tension side (ΔL _n <ΔM _n ), it is predicted that a hard layer exists ahead of the face K.

  Thereafter, the second process (second installation work, second initial value measurement work, second measurement work, second calculation work) and the natural ground prediction process are repeated. When the second step is performed a plurality of times, one or more relative displacements selected from existing relative displacements and the latest relative displacement may be used in the natural ground prediction step.

  In the natural ground prediction process, if the presence of a soft layer is predicted in the natural ground in front of face K, if necessary, advanced ground drilling such as advanced boring and underground elastic wave exploration, etc. Auxiliary methods such as construction and mirror bolts and countermeasures will be implemented.

  As described above, according to the natural ground situation prediction method of the present embodiment, the natural ground situation in front of the face K can be easily predicted by measuring the axial relative displacement of two points installed inside the tunnel T. Can do. Moreover, since the tunnel excavation work is not interrupted, it is possible to carry out the prediction of the natural ground situation in front of the face K as daily construction management.

  Since the target 1 and the laser displacement meter 2 can be installed simultaneously with the primary support work, the excavation work of the tunnel T is not affected.

  Understand the exact position, thickness, and strength characteristics of the soft layer in front of the face K by conducting advanced ground drilling such as advanced drilling and underground elastic wave exploration at the position where the soft layer is expected to exist. can do. Since it is possible to determine in advance the change of the support pattern and the use of the auxiliary construction method according to the result of exploration of the front ground of the face K, the workability is excellent.

The conventional mine displacement measurement using the total station and the method for predicting the ground ahead of the face involves surveying work, and it is necessary to interrupt the excavation work. There was a case. On the other hand, according to the natural ground condition prediction method of the present embodiment, after the laser displacement meter is installed, automatic measurement is possible, so that the excavation work of the tunnel T can be measured without interruption.
Moreover, since it can measure with high precision compared with a total station, prediction accuracy is also high.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and the above-described constituent elements can be appropriately changed without departing from the spirit of the present invention.

  For example, in the above-described embodiment, the case where the laser displacement meter is used has been described. However, the measuring instrument is limited to the laser displacement meter as long as it can measure the relative displacement at two points with high accuracy. Instead, for example, an extensometer or the like can be used.

  Further, the cross-sectional shape of the tunnel T is not limited.

Next, the result verified about the natural ground condition prediction method concerning this invention is demonstrated.
In this verification, it was verified by three-dimensional sequential excavation analysis that the natural ground condition (hardness of natural ground) in front of the face can be predicted by measuring the change in relative axial displacement between two points on the tunnel side.

The ground was assumed to be a linear elastic model, assuming a ground level DI as a hard layer and a ground level DII as a soft layer, and a model having a layer boundary changing from a hard layer to a soft layer. For the physical property values for analysis, representative values of mountain grades were adopted with reference to the tunnel numerical analysis manual (Japan Highway Public Corporation, 1998). Table 1 shows the ground physical properties for analysis.
The initial earth pressure is assumed to be an earth pressure equivalent to 100 m of earth covering at the tunnel top end position, and the lateral pressure coefficient is 1.0.

  In the analysis, it is assumed that every 1 m is excavated and the upper half and the lower half are excavated simultaneously. The primary support (spray concrete, steel support, rock bolt) is not modeled.

For tunnels penetrating the stratum boundary, the change in relative displacement at two points (face-side measurement point and well-hole-side measurement point) installed in the tunnel at the stratum boundary was calculated.
The distance between the two points (measurement distance a) was 20 m, and the change in relative displacement was calculated when the distance b from the face to the face-side measurement point was 10 m.

  FIG. 3A shows the analysis result of the relative displacement between two points accompanying tunnel excavation in this analysis model. However, in FIG. 3A, tension is positive and compression is negative.

  As shown in FIG. 3 (a), it can be seen that the axial relative displacement greatly changes to the compression side before the face reaches the formation boundary (0 on the horizontal axis). For example, when the distance d from the measurement cross section to the formation boundary is 21 m (distance e from the face K to the formation boundary is 11 m), the first relative displacement ΔL is 1.657 mm and the distance d is 11 m (distance e = 1 m). The second relative displacement ΔM is 0.692 mm, and the axial relative displacement (ΔL−ΔM) is 0.965 mm larger on the compression side.

  Here, since the accuracy of the high-precision laser displacement meter is about ± 0.2 mm, it is sufficiently possible to capture the difference in relative axial displacement (ΔL−ΔM). Therefore, it was proved that the ground in front of the face can be predicted in the strata changing from hard to soft by measuring axial relative displacement using a laser displacement meter.

FIG. 3B shows the result of calculating the change in relative displacement when the measurement distance a is 1 m for the same analysis model.
As shown in FIG. 3B, when the distance d is 21 m (distance e = 11 m), the first relative displacement ΔL is 1.383 mm, and when the distance d is 11 m (distance e = 1 m), the second relative displacement ΔM is The axial relative displacement (ΔL−ΔM) is increased by 0.077 mm toward the compression side.

  Here, since the resolution of the extensometer is 0.01 mm, it is sufficiently possible to capture the difference (ΔL−ΔM) in the axial relative displacement by using the extensometer.

  FIG. 4 shows the result of analyzing the change in relative displacement for an analytical model having a formation boundary that changes from the soft layer DII to the hard layer DI.

As shown in FIG. 4A, the relative displacement in the axial direction when the measurement distance a is 20 m is such that the first relative displacement ΔL is 6.775 mm when the distance d is 21 m (distance e = 11 m). On the other hand, the second relative displacement ΔM with a distance d of 11 m (distance e = 1 m) was 8.534 mm.
Therefore, it can be seen that the axial relative displacement (ΔL−ΔM) increases by 1.759 mm on the tension side due to the influence of the hard layer in front of the face.

  Further, as shown in FIG. 4B, even when the measurement distance b is 1 m, the first relative displacement ΔL when the distance d is 21 m (distance e = 11 m) is 4.666 mm, whereas the distance d Was 11 m (distance e = 1 m), and the second relative displacement ΔM was 4.774. Therefore, it can be seen that the axial relative displacement (ΔL−ΔM) increases by 0.108 mm toward the tension side due to the influence of the hard layer in front of the face.

  Therefore, according to the ground condition prediction method of the present invention, it is possible to predict the presence or absence of a hard layer or a soft layer in front of the face K by using the axial relative displacement between two points provided in the tunnel tunnel. It was proved that.

1 Target 2 Laser Displacement Meter K Face T Tunnel

Claims (2)

Setting the face side measurement point on the first measurement section, and setting the well side measurement point that is separated from the face side measurement point by a distance a from the face side,
An operation of measuring an initial value which is a positional relationship between the face side measurement point and the wellhead side measurement point;
When the face has reached a position separated from the measurement cross section by a distance b, an operation of measuring a measurement value that is a positional relationship between the face side measurement point and the wellhead side measurement point;
A first step of performing a work of calculating a relative displacement that is a difference between the initial value and the measured value;
After the face passes through the second measurement section, the second step of calculating the relative displacement in the same manner as the first step, and
A ground condition prediction method for predicting a ground condition ahead of a face based on a comparison between the relative displacement calculated in the first process and the relative displacement calculated in the second process. When the relative displacement calculated in the second step is larger on the compression side than the relative displacement calculated in the first step, it is predicted that a soft layer exists ahead of the face,
When the relative displacement calculated in the second step is larger on the tension side than the relative displacement calculated in the first step, it is predicted that a hard layer is present in front of the working face. The natural ground condition prediction method described.

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